A small proportion of the earth's surface is suitable for cultivation and much of this is due to the lack of water or the lack of suitable irrigation water due to the presence of impurities. In particular, there are large swathes of land in the Middle East where the salinity of the water which is present prevents any cultivation.
For example, Sabkahs (or salt flats) are large areas with ample access to water, and nutrient-rich soil, but where the salinity of the water prevents the cultivation of these areas.
It is desirable to create a system whereby these, and other arid areas, can be cultivated to support agriculture.